Flow Reserve Substudy Protocol: High-risk diabetics with CAC> 100 (n=10) and stratified random sample high risk non-diabetics (n=10) will be studied. The inclusion of subjects with an abnormal perfusion reserve is important, because this value identified subjects with high risk in the first phase of the study and therefore is used to select individuals with high risk of cardiac events that clinically would undergo invasive assessment of coronary anatomy. Perfusion imaging will then be the test that stratifies subjects into an additional higher risk than the CAC > 100. Selected patients identified as part of Specific Aim 2 will undergo a clinically indicated cardiac catheterization and baseline CFR study. Coronary angiography is the clinically accepted standard for evaluation and diagnosis of coronary artery disease.